The present disclosure relates to contrast imaging. More particularly, the present disclosure relates to methods for contrast imaging with which tissue motion is compensated to enhance the sensitivity to contrast agents by reducing motion-related image artifacts.
The use of ultrasound imaging has grown quickly due to the image quality achievable, its safety, and its low cost. Such imaging can be broken into two general categories: tissue imaging and contrast imaging. In contrast imaging, contrast agents, for example microbubbles of heavy gas encapsulated in rupturable shells of material, are introduced intravenously into the bloodstream. Due to their physical characteristics, contrast agents stand out in ultrasound examinations and therefore can be used as markers that identify the amount of blood flowing to or through the observed tissue. In particular, the contrast agents resonate in the presence of ultrasonic fields producing radial oscillations that can be easily detected and imaged. Normally, this response is imaged at the second harmonic of the transmit frequency f0.
Recently, it has been determined that tissue also produces harmonic responses which influence the images produced during contrast imaging. Several techniques have been developed which take advantage of the primarily linear response behavior of tissue to cancel or attenuate the linear tissue signals. In several of these techniques, multiple transmit lines are fired along the same line of sight into the body. The transmit waveform is modified (e.g., in terms of power, phase, or polarity) from line to line to produce a variation in the response received by the transducer. These data points are then processed to remove the influence of their linear components to yield data that primarily contains the non-linear response of the contrast agents.
Although the above-described techniques work well in removing the influence of stationary tissue, flash artifacts from moving tissue can degrade the resultant images. In particular, this movement causes decorrelation of the received echoes that is not compensated for with typical processing techniques. This degradation can be substantial, particularly where the heart is being imaged due to its frequent and rapid motions. Attempts have been made to reduce the effects of such movement by applying two-zero filters to the responses of the receive signals associated with the various transmit lines. However, this technique assumes perfectly linear tissue movement and therefore is not completely effective in removing the moving tissue signals.
From the above, it can be appreciated that it would be desirable to have a method for contrast imaging in which the response of moving tissue is effectively suppressed so as to enhance the imaging sensitivity of the contrast agents.
The present disclosure relates to apparatus and methods for imaging contrast agents within a patient""s body. The method generally comprises receiving echoed signals from the body, processing the received data to correct for motion effects, processing the received data to suppress tissue response, and imaging the contrast agents.
In a preferred embodiment, the ultrasound signal comprises a plurality of signal lines that have been modulated to have different transmit characteristics. In the preferred embodiment, the step of processing to correct for motion effects comprises measuring the Doppler shift of the received data to generate a motion estimate representative of tissue and contrast agent motion within the body. This motion estimate can then be used to time-correct the received data thereby compensating for motion effects in the received data.
The features and advantages of the invention will become apparent upon reading the following specification, when taken in conjunction with the accompanying drawings.